In order to survive in a world of pathogenic or potentially pathogenic microorganisms, higher organisms have evolved immune systems which can specifically recognize virtually any foreign substance through its characteristic molecules. This recognition frequently results in the production of specific proteins called antibodies which bind only to the foreign substance which induced their synthesis, causing the elimination of the invading microorganism. Occasionally an animal's immune system makes antibodies which recognize some of its own molecules, generating an autoimmune state that may affect the animal's health adversely.
The induction of specific antibodies in response to an immunogen involves the interaction of multiple cell types, including thymus-derived lymphocytes (T cells), macrophages, and bone marrow-derived lymphocytes (B cells). This is in contrast to the primary (IgM) immune response which does not include T cells. T cell dependent antigen responses are secondary responses. B cells possess surface immunoglobulin by which they are able to bind immunogens, the first step in their activation and clonal expansion. A single B cell expresses only one type of antigen-specific immunoglobulin. The site(s), region(s) or domain(s) of the immunogen to which the immunoglobulin binds is called a "B cell epitope." In the second step of B cell activation and expansion, T cells are activated through interaction with a site, region or domain of the immunogen called a "T cell epitopel" which is presented by B cells or other antigen-presenting cells. Once activated, the T cells provide positive signal(s) to the B cells to which the immunogen is bound and they proceed to differentiate and to produce and secrete antibody. Positive signals from the T cell include the secretion of lymphokines, and/or direct contact between the B cells and T cells. T cell epitopes may be different or more restricted in scope than B cell epitopes. As discussed above, in order for an immunogen to elicit T dependent antibodies, it must have epitopes recognized by both B and T cells.
Past attempts to treat antibody-mediated pathologies have involved both general and specific suppression of the immune response. General suppression has typically employed broad spectrum, nonspecific immunosuppressants such as cyclophosphamide or steroids. Because these nonspecific drugs suppress many aspects of the immune system, they limit its required and beneficial functions as well as the malfunction causing the condition being treated. They are thus used only with extreme caution and subject the patient to risk from secondary infections or other undesirable side effects.
Because of the disadvantages of general immunosuppression, methods for specifically suppressing an immune response to an immunogen without affecting the normal functions of the immune system are highly preferred for treating antibody-mediated pathologies. The present invention concerns compositions and methods for specifically suppressing the humoral response to immunogens.
Prior attempts to induce specific immunosuppression have focused on conjugating haptens and immunogens to nonimmunogenic polymeric carriers. Benacerraf, Katz and their colleagues used conjugates of haptens and antigens and copolymers of D-lysine and D-glutamic acid (formerly D-GL, hereinafter D-EK). Their initial studies involved conjugates of the synthetic hapten 2,4-dinitrophenyl (DNP) in guinea pigs and mice and showed the conjugates were capable of inducing humoral unresponsiveness. These initial studies were then extended to conjugates of other haptens and conjugates of immunogens. While the results with haptens were repeatable, and although their patents (U.S. Pat. Nos. 4,191,668 and 4,220,565) allege the approach is effective in inducing tolerance to immunogens, subsequent work has shown that conjugates of D-EK and immunogens do not provide a means for inducing humoral unresponsiveness to the immunogen. For instance, Liu et al., J. Immun. (1979) 123:2456-2464, report that subsequent studies of those conjugates demonstrate that the conjugates "do not induce unresponsiveness at the level of protein specific B cells." Similarly, Butterfield et al., J. Allergy Clin. Immun. (1981) 67:272-278, reported that conjugates of ragweed immunogen and D-EK actually stimulated both IgE and IgG responses to the immunogen.
This subsequent work and other data dealing with conjugates of nonimmunogenic polymers and immunogens (Sasaki et al., Scand. J. Immun. (1982) 16:191-200; Sehon, Prog. Allergy (1982) 32:161-202; Wilkinson et al., J. Immunol. (1987) 139:326-331, and Borel et al., J. Immunol. Methods (1990) 126:159-168) appear to indicate that the anergy, if any, obtained with such conjugates is due to suppression by T cells to directly suppress the immune response.
Several other references deal with conjugates of nonimmunogenic polymers and DNA. See U.S. Pat. No. 4,191,668; U.S. Pat. No. 4,650,625; J. Clin. Invest. (1988) 82:1901-1907; and commonly owned U.S. patent application Ser. No. 07/494,118 (now U.S. Pat. No. 5,162,515). As a whole, these references indicate that these DNA conjugates may suppress the production of antibodies to the lupus autoimmunogen. It should be noted in this regard that DNA is not immunogenic and does not possess T cell epitopes.
In sum, applicants believe the prior art shows that antibody production to conjugates of nonimmunogenic stable polymers and haptens or DNA, neither of which have T cell epitopes, may provide B cell unresponsiveness. Applicants also believe that conjugates of immunogens do not provide B cell unresponsiveness but may activate T cells to directly suppress the immune response.